1. Field of the Invention
The present invention is directed to crosslinked interfacially polymerized polyester amide membranes, their preparation and use in organic liquid separations.
The membrane is prepared by producing a prepolymer by reacting a dianhydride (or its corresponding tetra-acid or di acid-diester) preferably dianhydride or its corresponding tetra-acid with a polyester diol in a 2:1 to 1.05:1 mole ratio of anhydride or carboxylic acid group to polyester hydroxyl groups. The resulting prepolymer is then reacted with excess thionyl chloride which converts all unreacted anhydride groups and carboxylic acid groups of the prepolymer to acid chloride groups. This acid chloride derivative is dissolved in an organic solvent and reacted interfacially with a diamine dissolved in an aqueous solvent. The organic and aqueous solutions can be just floated one over the other to create an interface or a substrate can be wash coated with one or the other of the solutions, drained, then wash coated with the complementary solution. In either case a membrane forms at the interface between the organic and aqueous solutions due to reaction between the diamine and the acid chloride capped prepolymer. Upon completion of the reaction, the formed membrane is dried at between about 50.degree. to 150.degree. C., preferably 80.degree.-120.degree. C., most preferably about 80.degree.-100.degree. C.
The resulting membrane is useful for organic liquid mixture separations such as the separation of aromatic hydrocarbons from mixtures of same with non-aromatic hydrocarbons; the separation of isoparaffins from mixtures of same with n-paraffins; the separation of olefins from mixtures of same with paraffins; the separation of oxygenates such as mixtures of ethers and alcohols, e.g., methyl tert butyl ether/methanol etc., under pervaporation or perstraction conditions, preferable pervaporation conditions.
2. Discussion of the Related Art
U.S. Pat. No. 4,277,344 describes interfacially synthesized reverse osmosis membranes. The membranes are made from crosslinked interfacially polymerized aromatic polyamides, particularly poly(arylene-polyamine aromatic-polycarboxylamides) such as poly (phenylenediamine trimesamide). The aromatic polyamides are preferably synthesized directly from an essentially monomeric polyacylhalide (at least tri- or higher in acyl functionality) and an essentially monomeric arylene polyamine with a measurable water solubility. A porous support layer is coated with the polyamine component (e.g., an aqueous solution of phenylene diamine); the thus-coated support is contacted with the polyacyl halide component (e.g., trimesoyl chloride), thereby initiating the interfacial polymerization in-situ on the support. The resulting membrane is dried to provide a composite membrane comprising the polyamide laminated to the porous support. The membranes are used for the reverse osmosis desalination of aqueous solutions.
U.S. Pat. No. 4,946,594 describes a crosslinked copolymer composition in which the copolymer is derived from an aliphatic polyester diol, a dianhydride and a diisocyanate crosslinking agent. The resulting membrane is useful for separating aromatic hydrocarbons from mixtures of same with non-aromatic hydrocarbons.
U.S. Pat. No. 4,990,275 relates to a copolymer composition comprising a hard segment of a polyimide and a soft segment of an oligomeric aliphatic polyester. Membranes made from the copolymer are useful for aromatic/saturates separations. The polyimide is derived from a dianhydride having between 8 an 20 carbons and a diamine having between 2 and 30 carbons while the oligomeric aliphatic polyester is a polyadipate, polysuccinate, polymalonate, polyoxalate or polyglutarate.
U.S. Pat. No. 5,049,281 is directed to a multi-block copolymer, the membrane made from such copolymer and the use of the membrane for separation. The multi-block copolymer can comprise a first prepolymer made by reacting a diamine with an epoxy in a diamine to epoxy mole ratio of 2.0 to 1.05 resulting in a diamine end capped prepolymer which is then chain extended with a second compatible prepolymer which can be a dianhydride or its corresponding tetra acid or diacid-diester combined with a polyester in a dianhydride to polyester mole ratio of about 2.0 to 1.05. In the text it is stated that if the diacid-diester or tetraacid derivative of the dianhydride is used they must first be converted to species that will react with diamines or polyesters. This can be done by conversion of the tetra-acid or diacid-diester into an acid chloride by derivatization using thionyl chloride. If this acid chloride is reacted with a diamine an amide acid is formed which when heated or chemically cyclized forms an imide. If the acid chloride is reacted with a polyester the product which results is itself an ester which requires no further curing. This patent, however, does not teach the formation of an interfacially polymerized membrane or the use of such a membrane for separations.
See also U.S. Pat. No. 5,039,422.